The enzymatic nature of the process for releasing acid when E. coli membranes are oxidized through a voltage range of 315 to 340 mV is indicated by the necessesity of providing E. coli protein, the loss of activity accompanying boiling of the protein fraction and the fact that mitochondrial protein has a different degree of activity in the system. Potentiometric titrations of beef heart mitochondria indicate that cytochrome C1 exists as two 2 electron transferring species rather than as a single 1 electron species as now believed. Rapid scan spectroscopy of the phenomenon of the oxidant-induced reduction of motochondrial cytochrome b reveals that only cytochrome b-566 participates in the reaction and not b-562. This is in contrast to contemporary schemes which place both b-cytochromes in the Q-cycle loop.